1. Field of the Invention
This invention relates to a cooling installation for a machine tool or the like, having a circulation system in which coolant circulates, wherein the coolant is conducted to a tempering device of the machine tool, wherein a metering unit is assigned to the circulation system, by which an external coolant can be metered to the coolant circulating in the circulation system, and wherein the metering unit can be controlled by a control device.
2. Description of Related Art
Such cooling installations are used, for example, to cool machine beds of precision lathes or precision milling machines. With the tempering device, the machine bed is maintained at a temperature which corresponds to the ambient temperature. In this case the deviation of the temperature in the tempering device from the ambient temperature is only allowed to be very small, preferably the deviation may be {fraction (2/10)} to {fraction (3/10)} of a degree Celsius. At present, a circulation system in which coolant circulates is used in connection with such cooling installations. In this case the temperature of the coolant is selected so that the ambient temperature is reached in the tempering device. If the temperature in the circulation system reaches an impermissibly high value, the control device detects this situation. Thus the control device controls the metering unit, for which purpose external cooling medium is metered into the inflow, for example upstream of the machine tool, of the circulation system. In this case the external coolant has a lower temperature than the coolant conducted in the circulation system. A brief intense fall below the temperature in the inflow is caused with this type of cooling, which causes a sudden temperature drop in the tempering device.
It is one object of this invention to provide a cooling installation of the type mentioned above for maintaining a constant temperature level in the tempering device.
This object is achieved because the circulation system has a buffer tank, through which the coolant is conducted, and the metering unit meters the external coolant into the return flow coming from the tempering device and into the circulation system upstream of the buffer tank.
If the temperature level in the circulation system is detected as impermissibly exceeded, the cold external coolant is metered into the return flow and thereafter can be mixed in the buffer tank with the coolant conducted in the return flow, because of which an even temperature level is generated. A sudden temperature drop in the tempering device thus can be dependably prevented.
In one preferred embodiment of this invention, the cooling installation has a refrigeration circuit with an evaporator connected to a cooling circuit, into which the external coolant is conducted. A connection between the cooling circuit and the circulation system can be made with the metering unit. With the refrigeration circuit there is always sufficient external coolant available at the metering unit.
To provide a self-sufficient system, which is closed in itself, in one embodiment of this invention, a partial tank is assigned to the buffer tank, wherein the buffer tank is connected with the partial tank via an overflow device, and a cooling circuit, which is connected with the circulation system via the metering unit, extends through the partial tank. When using a refrigeration circuit for cooling the external coolant, the temperature of the external coolant in the cooling circuit is monitored with a temperature sensor. The temperature sensor is a component of a control circuit, which activates the compressor of the refrigeration circuit when the temperature falls below a reference variable and shuts it off when a predetermined value is exceeded. An energy-saving operation is effected through this control circuit.
The circulation system preferably has a heat exchanger, by which a consumer can be cooled. A machine control can be used as a consumer, for example, which in the end is used for controlling the machine tool to be cooled. Thus the complete cooling of the entire machine tool is provided because of a single cooling installation.
In one preferred embodiment of this invention, an ambient temperature sensor, which is assigned to the tempering device, and a buffer tank temperature sensor, which is arranged in the coolant of the buffer tank, are connected to the control device. The control device has a control circuit which forms a differential temperature between the ambient temperature sensor and the buffer temperature sensor and controls the metering unit as a function of the differential value obtained. In this case the ambient temperature sensor can be arranged in such a way that it is placed in the immediate vicinity of the tempering device and measures the temperature of the surrounding ambient air.
The metering unit is preferably designed as a solenoid valve, which can be opened or closed, clocked by the control device.
To reduce the parts cost, the buffer tank and the partial tank are formed by a common tank and are separated from each other by a bulkhead, wherein the bulkhead forms an overflow device.
For reducing the parts cost the control device should be used to set the temperature of the external coolant to a lower temperature than the temperature of the coolant present in the circulation system.
In another embodiment of this invention, the flow in the cooling circuit is monitored by a flow monitor for reasons of operational dependability.